Plan B: Literature Review (Part II)


Twelve participants of Group A did not ovulate, and LNG significantly (P<0.05) shortened the mean length of the cycle compared to that of control… These participants were, therefore, excluded from the remainder of the analysis. In the three remaining participants of Group A, LNG administration did not modify significantly the length of that cycle… In Groups B, C, and D, no modifications were noted on cycle length… Follicular phase length was significantly longer only three ovulatory participants of Group A… In the remaining groups, no differences were noted in follicular phase length between treated and control cycles… In all participants of Group B and C, there were no differences in luteal phase length between the treated and control cycles. The three LNG-treated participants with normal cycle length in Group A and all treated participants in Group D had a significant shortening…of the luteal phase.

…12 participants of Group A had anovulatory cycles following LNG…All participants in Groups B, C, and D had ultrasonographic findings of FR, and LNG administration did not modify the day of the cycle at which FR occurred…

Twelve of the fifteen participants in group A (80%) did not ovulate (presumably due to the action of LNG). The remaining three ovulated, but had shorter-than-normal luteal phases. All of the Group B, C, and D participants showed evidence of follicular rupture (and therefore ovulation). Groups B and C showed no change in luteal phase length but Group D had short luteal phases.

With the exception of Group D, the mean serum ILP4AUC [integrated luteal progesterone area under the curve] in all remaining groups was similar when compared with the control cycle… In Group D, participants presented significantly lower daily serum P4 concentrations and ILP4-AUC when compared with those in control cycles…

That is, while ovulatory cycles in both Groups A and D had shortened luteal phases, Group A had longer follicular phases, but Group D had suppressed progesterone levels during the luteal phase. This is indicative of possible luteal insufficiency in Group D.

In both control and treated cycles, neither inflammatory, reactive, nor other abnormal features in [endometrial] tissue specimens were observed…[E]ndometrial morphology corresponded, according to both LH surge and FR, to the expected day…at which the biopsy was obtained.


No significant changes were observed between treated and control specimens in any of the studied [endometrial] parameters. No significant differences among any of the groups were observed. Of particular importance was the finding that the predecidual changes as evaluated by the presence of prominent spiral arteries, which are considered crucial for implantation [24], were not altered by LNG.

In short, in this experiment LNG did not seem to make the endometrium hostile to embryo implantation. This is noteworthy because in those cases where LNG shortened the luteal phase, one might expect its normal function would be impaired. If that is the case, it doesn’t seem to be through modification of the endometrium.

Comments 8

  1. Stuff wrote:

    Does anyone know whether 45 participants is statistically appropriate to draw generalizations from their findings? I know there’s all kinds of ethical and logistical problems with obtaining more, but I seem to remember from way, way back in pharmacy school tests you could perform to give more credibility to your study by showing the group sizes were appropriate. 45 just seems kind of small to me. Otherwise the study seems well-done.

    Posted 23 Oct 2006 at 5:44 pm
  2. Jerry wrote:

    Fallopian tube dysfunction is another postfertilization effect that has been mentioned. Have you seen anything on that? (And did that recent JAMA review I sent you prove at all useful?)

    Stuff: for a fairly involved human study, 45 isn’t necessarily too bad…

    Posted 23 Oct 2006 at 10:14 pm
  3. Funky Dung wrote:

    I haven’t read anything more current than 2001 about fallopian tube dysfunction. The Croxatto, et al., paper I presented in Part I had this to say:

    Alterations in embryo transport through the fallopian tube or uterus following EC, are also difficult to explore. Delayed transport or retention in the tube cannot be excluded a priori, although no increased incidence of tubal pregnancy has hitherto been reported with the current methods. Accelerated transport through the tube appears unlikely since neither estradiol nor progesterone given in high doses right after ovulation have this effect in women [102].

    Posted 24 Oct 2006 at 9:06 am
  4. cjmr wrote:

    45 participants would be too small for a safety or efficacy study, but for a ‘method of operation’ study that is a reasonable number.

    Posted 26 Oct 2006 at 7:58 pm
  5. Lightwave wrote:

    Maybe someone with a statistical background can help me out here. I know that any number of test subjects can be statistically significant depending on the desired confidence level one wants in the results. If we had statistics on the number of EC users, would we not be able to calculate the “confidence interval” for 45 test subjects? Thus we would know the confidence with which we can say these results apply to the general population.

    Would it not be fair to say that any confidence in these results (> 0%) is better than having no data and hence no confidence? i.e. the conclusions from data presented here is far more likely to be accurate than conclusions based on conjecture and assumptions on the effects of EC?

    Posted 30 Oct 2006 at 9:47 am
  6. Mariana wrote:

    Based on that study, I would say Plan B does not affect the endometrial lining, but it does affect the length of the luteal phase due to progesterone insufficiency. 80% of those taking the pill before ovulation and before the LH surge failed to ovulate, those who took it after the LH surge or right after ovulation noticed no effect.

    Given the pregnancy “prevention” rate of Plan B is 89% (including people who had sex after ovulation), and this study showed a prevention of ovulation of 80%, I would NOT draw the conclusion that Plan B was primarily abortifacient. I would recommend any woman taking Plan B to monitor herself for ovulation and supplement with progesterone to prevent a short luteal phase. I would not recommend women taking Plan B on ovulation day or later, because it is either unnecessary, inneffective, or potentially abortifacient.

    To me, it seems that from the study that the primary mode of action of Plan B is to prevent ovulation, not to damage the endometrium (no evidence of this mode of action). It can shorten the luteal phase, but that seems to be due to a crash in hormones, and theoretically could be prevented through progesterone supplementation.

    Of course, the results of one small study are not conclusive in any way.

    Based on this document: It would be useful to know exactly when Plan B acts as an abortifacient and when it acts simply as a contraceptive. If the abortifacient action of Plan B is simply to shorten the luteal phase, the combination of a transvaginal ultrasound and progesterone supplements would be a good theoretical protocol to follow to avoid the misuse of the drug in cases of sexual assault.


    Posted 04 Nov 2006 at 8:35 pm
  7. Raluka wrote:

    Please tell me what happened to the women from group A who took Postinor in day 10 of their cycle and still ovulated. I read on your blog that they had normal cycle length, while the luteal fhase was much shorter. Are this data from a study, is it written tehre or is only something you assumed? Thank you.

    Posted 18 Nov 2008 at 4:07 am
  8. Kabubu wrote:

    Day one of my last period was 12/26. I was raped on 1/1 and took plan B on 1/4. Today, 1/11, day 17 of my cycle, I had my period. My cycle is usually about 29 days long, give or take a 2-3 days. I felt none of the warning signs that generally accompany my period. In reading this, I am inclined to think that plan B may be the cause for this unusually short cycle. I will continue to monitor myself for any abnormalities and relate this to my doctor if the need to do so arises.

    Posted 12 Jan 2010 at 12:19 am

Trackbacks & Pingbacks 2

  1. From luminousmiseries on 24 Oct 2006 at 4:01 am

    brings us “Some thoughts on Suffering.” Recently Ales Rarus looked at a couple literature reviews about the methods of action of Plan B emergency contraception (levonorgestrel, LNG). This time it’s Plan B: Literature Review (Part II): On the the mechanisms of action of short-term levonorgestrel administration in emergency contraception (Durand, et al., 2001) If the blog name The Kitchenmadonna doesn’t make you want to click on through then maybe the post title

  2. From Participatory Bible Study Blog » Blog Archive » Christian Carnival CXLV on 25 Oct 2006 at 2:36 pm

    […] In the field of medicine and ethics, from Ales Rarus, we have Plan B: Literature Review (Part II). This is the second post in a series. Last time I looked at a couple literature reviews about the methods of action of Plan B emergency contraception (levonorgestrel, LNG). This time I’m presenting On the the mechanisms of action of short-term levonorgestrel administration in emergency contraception (Durand, et al., 2001). […]

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